The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Three on trial for WA man's murder

David Liam Johnson was bashed, run over by a car and shot by three men he barely knew during a "church night" among a gang that was recruiting members, a Perth trial has heard.

Alexander James Stephens, Nathan Michael Beckton and Angus William John Ritchie are on trial in the West Australian Supreme Court, accused of murdering the 32-year-old man in Swanbourne in March last year.

Prosecutor Carmel Barbagallo said in her opening address on Wednesday that Mr Johnson was invited by his friend to attend the gathering, which the gang called "church nights", before he became involved in an argument with Beckton who threatened him with a meat cleaver.

Mr Johnson later hid under a utility at the front of the house and his friend left, believing Mr Johnson had gone.

But Mr Johnson was soon dragged out from under the vehicle and stomped on, laughed at, verbally abused and kicked, the court heard.

Stephens and Ritchie drove away to look for Mr Johnson's friend but instead returned with a sawn-off shotgun.

Ms Barbagallo said Stephens ran over Mr Johnson and then said "f*** this c*** is still breathing" before throwing a concrete slab on his head.